Commands

Chat
/party /group /p /whisper /w /tell /t /reply /r (technically also a whisper, but does function a bit different in who it auto-fills name with) /guild /g /all (just sets the channel to the "normal" channel which will always default to where you currently are) /friend /unfriend /help /friends (opens the Social screen) /ignore /block /invite (to party, not to guild)

Commands as of version "++dauntless+rel-1.4.0-CL-230247" (PC):
Exact version identifier (Version.txt): "dauntless_rel-1.4.0_Shipping_2020-09-09_20-18-33_230247"

Where a player handle is required as a parameter, you can use  completion.

The game will propose matching command names and matching handles as you type. You can select from the offered lists by "up" / "down" / "enter" - however this might be called on your platform.